Yes, John Denver's plane was not well built, but the accident was clearly due to his own careless stupidity. Read the NTSB accident report and I expect that you will agree.

Shoddy maintenance with certificated aircraft is NOT a common problem. Home builts bypass the certification and maintenance requirements, so what can one expect? Don't get me wrong. People have all the right in the world to build and fly aircraft as they choose.

I personally have no desire to fly any home built or experimental aircraft.